Systems and methods for vehicle sound enhancement

ABSTRACT

Embodiments are disclosed for enhancing engine sound. An example method for a vehicle comprises acquiring a signal including harmonic content generated by an engine of the vehicle, upmixing the signal into a plurality of channels for a given number of engine orders, adjusting an order filter for each engine order of the given number of engine orders based on operating conditions of the engine, filtering each channel of the plurality of channels with the corresponding order filter, mixing the filtered channels into a mono output, and outputting the mono output to at least one speaker in the vehicle. The mono output is delayed based on a position of the at least one speaker such that an occupant of the vehicle perceives the mono output as originating from the engine.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 17/199,288, entitled “SYSTEMS AND METHODS FORVEHICLE SOUND ENHANCEMENT,” and filed on Mar. 11, 2021. U.S.Non-Provisional patent application Ser. No. 17/199,288 claims priorityto U.S. Provisional Application No. 62/990,358, entitled “SYSTEMS ANDMETHODS FOR VEHICLE SOUND ENHANCEMENT,” and filed on Mar. 16, 2020. Theentire contents of the above-listed applications are hereby incorporatedby reference for all purposes.

FIELD

The disclosure relates to vehicle sound enhancement.

BACKGROUND

A vehicle may include an internal combustion engine for generatingmechanical energy to drive the vehicle. The configuration of the engine,such as the arrangement of engine cylinders and valve timing for intakeand exhaust valves, impacts the sound generated by the engine. Forvehicles with different engine configurations, even with a same numberof engine cylinders, the vehicles may sound substantially different.Some drivers may desire a certain engine sound. For example, somedrivers may prefer a louder, raspier engine sound and thus may prefer todrive a sports car, while other drivers may prefer a smoother andquieter engine sound.

Various methods exist for enhancing the sound of an engine based on adesired engine sound. For example, an engine sound may be digitallysynthesized based on current operating conditions, such as therevolution per minute (RPM) of the engine. However, for sporty engineswith rapidly-changing RPM, such synthesis can sound artificial andunresponsive. Meanwhile, traditional acoustic sound synthesis requires adelicate tuning process to design layers of narrowband and broadbandsound to be authentic.

SUMMARY

In order to enhance the engine sound while maintaining authenticity, theoriginal engine sound may be measured and the engine harmonics may beenhanced in real-time by filtering the spurious content. A morerealistic sound enhancement in the vehicle cabin may thus be obtained byusing the original engine sound as a source, instead of a synthesizedsignal. To capture the original engine sound, a sensor such as anaccelerometer is installed directly onto the engine block, whichcaptures the harmonic content originally generated by the engine,avoiding all other sound artifacts occurring close to the engine whichwould be captured by a sound pressure sensor such as a microphone.

Embodiments are disclosed for enhancing engine sound. An example methodfor a vehicle comprises acquiring a signal including harmonic contentgenerated by an engine of the vehicle, upmixing the signal into aplurality of channels for a given number of engine orders, adjusting anorder filter for each engine order of the given number of engine ordersbased on operating conditions of the engine, filtering each channel ofthe plurality of channels with the corresponding order filter, mixingthe filtered channels into a mono output, and outputting the mono outputto at least one speaker in the vehicle. The mono output may be upmixedinto a plurality of channels for output to a respective plurality ofspeakers in the vehicle, and delays may be separately applied to eachchannel to create a spatial effect within the cabin of the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be better understood from reading the followingdescription of non-limiting embodiments, with reference to the attacheddrawings, wherein below:

FIG. 1 is a block diagram of an example system within a vehicle forenhanced vehicle sound synthesis, in accordance with one or moreembodiments of the present disclosure;

FIG. 2 is a block diagram illustrating an example method for enhancedvehicle sound synthesis, in accordance with one or more embodiments ofthe present disclosure;

FIG. 3 is a graph illustrating a bank of bandpass filters guided by RPMfor filtering sensor measurements, in accordance with one or moreembodiments of the present disclosure;

FIG. 4 is a block diagram illustrating an example digital signalprocessing chain for enhanced vehicle sound synthesis, in accordancewith one or more embodiments of the present disclosure;

FIG. 5 shows example spectrograms before and after filtering, inaccordance with one or more embodiments of the present disclosure.

FIG. 6 is a block diagram illustrating another example digital signalprocessing chain for enhanced vehicle sound synthesis, in accordancewith one or more embodiments of the present disclosure;

FIG. 7A shows a set of graphs illustrating example lookup tables fordetermining an example first order filter for a first order, inaccordance with one or more embodiments of the present disclosure;

FIG. 7B shows a set of graphs illustrating example lookup tables fordetermining an example second order filter for a second order, inaccordance with one or more embodiments of the present disclosure;

FIG. 7C shows a set of graphs illustrating example lookup tables fordetermining an example third order filter for a third order, inaccordance with one or more embodiments of the present disclosure;

FIG. 7D shows a set of graphs illustrating example lookup tables fordetermining an example fourth order filter for a fourth order, inaccordance with one or more embodiments of the present disclosure; and

FIG. 8 shows a high-level flow chart illustrating an example method forenhanced vehicle sound synthesis, in accordance with one or moreembodiments of the present disclosure.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of an example system 100 within a vehicle 132for enhanced vehicle sound synthesis. The system 100 may be locatedand/or integrated within the vehicle 132. The system 100 includes one ormore vehicle systems 140 such as an engine 142 of the vehicle 132. Thevehicle system 140 further includes a sensor 144, such as anaccelerometer, mounted to the engine 142 to measure the harmonic contentgenerated by the engine 142. By mounting the sensor 144 directly ontothe engine 142, the sensor 144 may avoid measuring or recording othersound artifacts occurring close to the engine 142, which would becaptured by an airborne sound-pressure sensor, such as a microphone.

The system 100 further includes a computing system 150 comprising atleast a processor 152 and a memory 154. The processor 152 may compriseone or more central processing units (CPU), a graphics processing units(GPU), digital signal processors (DSP), application specific integratedcircuits (ASIC), field programmable gate arrays (FPGA), analog circuits,or combinations thereof. The memory 154 may include one or more of amain memory, a static memory, and a dynamic memory. The memory 154 maycomprise a non-transitory memory device. The memory 154 may furthercomprise one or more volatile and/or non-volatile storage mediaincluding but not limited to random access memory, read-only memory, andthe like. Executable instructions or software may be stored in thememory 154 that may be executed or processed by the processor 152.

The computing system 150 may communicate with one or more elementswithin the vehicle, including but not limited to vehicle systems 140such as the engine 142 connected via an in-vehicle interconnect, such asController-Area-Network (CAN) bus 136. It should be understood that anysuitable number and/or combination of interconnects may be used topermit communication between the computing system 150 and variousin-vehicle components, including but not limited to CAN buses, MediaOriented Systems Transport (MOST) buses, Ethernet-based interconnects,and so on. Interconnects may communicate directly with in-vehiclecomponents and/or may communicate with such components via interveningprocessors. In some embodiments, one or more in-vehicle components maycommunicate directly with the computing system 150 without or inaddition to communicating with the computing system 150 via the CAN bus136. For example, a sensor 144 mounted on the engine 142 may directlycommunicate measurements to the computing system 150. The sensor 144 maycomprise an accelerometer configured to measure acceleration, forexample by measuring vibrations of the engine 142, as describedhereinabove. Further, the computing system 150 may receive measurementsof various operating parameters or operating conditions of the vehiclesystem 140 such as engine load or torque, engine RPM, gas pedalposition, and so on, as CAN messages via the CAN bus 136.

The computing system 150 is communicatively coupled to audio speakers164 distributed throughout the vehicle 132 via an audio amplifier 162.As described further herein, the computing system 150 is configured toperform digital signal processing of the signal from the sensor 144,based on CAN messages from the CAN bus 136, in order to enhance enginesounds. The enhanced engine sounds are output, via the audio amplifier162, to the plurality of audio speakers 164 in order to enhance theoriginal engine sound of the engine 142 within the cabin of the vehicle132.

FIG. 2 is a block diagram illustrating an example method 200 forenhanced vehicle sound synthesis. A vehicle 202 may comprise a motorvehicle, for exampling, including drive wheels and an internalcombustion engine. The vehicle 202 may comprise a road automobile, amongother types of vehicles. In some examples, the vehicle 202 may include ahybrid propulsion system including an energy conversion device operableto absorb energy from vehicle motion and/or the engine and convert theabsorbed energy to an energy form suitable for storage by an energystorage device. The vehicle 202 may comprise the vehicle 132 describedhereinabove, for example.

The internal combustion engine of the vehicle 202 may include one ormore combustion chambers which may receive intake air via an intakepassage and exhaust combustion gases via an exhaust passage. Theinternal combustion engine, or simply the engine, may comprise afour-cycle engine, wherein power is obtained via an intake cycle, acompression cycle, an explosion/expansion cycle, and an exhaust cycle.The engine may comprise a plurality of combustion chambers or cylinders,which may be arranged in series, in a V shape, or in parallel, asillustrative examples. While the four cycles are performed in theengine, a piston of the engine is raised or lowered, thereby rotating acrankshaft mechanically connected to the piston. The rotation of thecrankshaft is transferred to wheels of the vehicle 202, thereby movingthe vehicle 202 forward or backward. The crankshaft thus continuouslyrotates in accordance with repeated cycles of the engine, wherein therate of rotations of the crankshaft or the revolutions per minute (RPM)of the crankshaft is referred to as the engine RPM. The engine RPM mayvary by increasing or decreasing throughout the operation of the vehicle202.

As shown, an accelerometer (ACC) 208 may be located or integrated intothe vehicle 202, for example by mounting the accelerometer 208 onto theengine of the vehicle 202. The accelerometer 208 measures vibrations ofthe engine over time. The combustion cycles described hereinabove causevibration of the engine, such that the engine vibrates with a variety offrequencies according to various factors including but not limited toengine RPM, torque, throttle position, vehicle velocity, amount of fuelinjection, and so on. For example, as the engine RPM or simply RPMincreases, the vibration frequency increases. As an illustrative andnon-limiting example, a signal 212 acquired via the accelerometer 208during operation of the engine of the vehicle 202 may comprise a measureof loudness (measured in decibels) as a function of frequency and RPM,wherein the intensity of vibrations in a given frequency band may behigher or lower than the intensity of vibrations in a differentfrequency band.

Further, engine sound is generated by the combustion within the engineas well as the vibration. While the engine generates a range offrequencies, especially under load, the root note of the engine sound isdefined by a dominant frequency. As an illustrative example, for asix-cylinder engine operating at 1800 RPM, which corresponds to afrequency of 30 Hz, with a four-stroke cycle, each cylinder fires onceevery two crankshaft rotations. Therefore, as the number of ignitionevents per crankshaft revolution is three for a six-cylinder engine, thedominant frequency at 1800 RPM is 90 Hz. As the dominant frequency isthree times the frequency of engine rotation, the dominant frequency isa third engine order or simply third order for a six-cylinder engine.Similarly, the dominant frequency for a two-cylinder engine is the firstorder, the dominant frequency for a four-cylinder engine is the secondorder, the dominant frequency for an eight-cylinder engine is the fourthorder, the dominant frequency for a ten-cylinder engine is the fifthorder, and so on.

In order to enhance the engine sound, the vibrations recorded by theaccelerometer 208 may be filtered with a digital signal processingmodule 216 configured to enhance the engine sound. For example, asdepicted by the graph 300 of FIG. 3 , a signal 305 acquired by theaccelerometer 208 (e.g., the signal 212) may be filtered with aplurality of bandpass filters 310 wherein the center frequency of thebandpass filters is guided by the RPM. In particular, each bandpassfilter of the plurality of bandpass filters 310, such as the bandpassfilter 312, the bandpass filter 314, and the bandpass filter 316, may beapplied to a corresponding mode of the vibration signal to enhance theengine sound. Furthermore, the gain and the Q factor of the filters maybe tuned based on operating conditions such as gas pedal position,engine load or engine torque, throttle position, and so on. Thus, themethod 200 includes capturing the original engine sound 212, or morespecifically the harmonic content originally generated by the engine,with the accelerometer 208 and enhancing the engine sound with abandpass filter for different modes of the original engine sound 212.The enhanced engine sound 218 is then provided to one or more speakers220 positioned within the vehicle 202 to play back the enhanced enginesound 218 to occupants of the vehicle 202. The method 200 thus creates arealistic sound enhancement in the cabin of the vehicle 202 by using theoriginal engine sound 212 as a source, rather than a synthesized signalsuch as oscillators or a stored sound bank.

FIG. 4 is a block diagram illustrating an example digital signalprocessing method 400 for enhanced vehicle sound synthesis. The digitalsignal processing method 400 may be implemented via the computing system150 described hereinabove, for example, as the DSP module 216.

Sensor input 402 comprises the signal from the sensor 144 or theaccelerometer 208 as described hereinabove. That is, the sensor input402 comprises measurements of the vibrations of the engine 142. As thesensor 144 may sample the engine vibrations at a high rate, the sensorinput 402 is downsampled 404 to a lower sampling rate by a factor M. Thedownsampled signal is then upmixed 406 from a single channel to a numberof channels corresponding to a number of engine orders for enhancement.In an illustrative and non-limiting example, the downsampled signal isupmixed 406 or converted from a single channel to four channels of thesame downsampled data. Each channel is then input to a correspondingorder filter 420. For example, as depicted, the order filters 420 mayinclude four order filters (e.g., bandpass filters) for four differentengine orders. The engine orders may correspond to whole orders, halforders (e.g., 2.5 order), and so on, depending on the particularconfiguration of the engine (e.g., the arrangement of the cylinders andthe tuning of the various intake/exhaust valves) and thus the desiredorders for enhancing. The orders are thus tuned to the firing order ofthe engine as described hereinabove. It should be appreciated that themethod 400 may be adapted for a number of channels and a correspondingnumber of order filters other than four channels and four order filters.For example, the number of channels may be greater than or less thanfour in some examples, and so the number of engine orders and orderfilters may be greater than or less than four in such examples.

A plurality of CAN messages 412 or CAN signals, corresponding tomeasurements of RPM and torque, are also obtained via the CAN bus, asdepicted, for the signal processing method 400. The CAN signals 412 areused to adjust each order filter according to the current operatingconditions of the engine. For example, the gain, Q value, and centerfrequency (f) for each order may be determined based on the CAN signals412 to adjust the order filters 420. In particular, the RPM and thetorque are used to determine, via a three-dimensional gain lookup table414 that returns a gain value for a pair of RPM and torque measurements,a gain value for each order filter. Further, the RPM and the torque areused to determine, via a three-dimensional Q value lookup table 416 thatreturns a Q value for a pair of RPM and torque measurements, a Q valuefor each order filter. Further, the RPM is used to determine, via anorder lookup table 418, a center frequency (f) for each order based onthe RPM measurement. Thus, the order filters 420 are adapted, for eachorder, based on the current operating conditions. The lookup tables 414,416, and 418 are tunable to provide desired enhancement of differentorders for different combinations of operating conditions.

Thus, the order filters enhance the engine harmonics by filtering outspurious content. As the engine harmonics vary their frequenciesproportionally with RPM, the filters should be reactive enough to filterprecisely without stability issues when a new CAN parameter arrives.Therefore, state variable filters may be used for the order filters 420.As another technique, filter coefficient morphing may be used to updatethe order filters as the operating conditions change. For example, totransition from an initial filter (based on a first set of operatingconditions or a first set of RPM and torque measurements) to a targetfilter (based on a second set of operating conditions), the filtercoefficients of the two filters may be blended according to a specifiedblend factor. Thus, the bandpass filters comprising the order filtersshift in frequency, gain, and quality factor Q as a function of the RPMand torque measurements, wherein upon receiving the parameters (i.e., f,Q, and G), the filter coefficients are calculated via coefficientmorphing.

As an illustrative and non-limiting example, FIG. 5 shows examplespectrograms before and after filtering, including an originalspectrogram 510 prior to filtering and a filtered spectrogram 520 afterfiltering, wherein the spectrograms 510 and 520 depict the spectrum offrequencies over time or samples. In particular, the originalspectrogram 510 is obtained for a V8 engine during acceleration whereinRPM is ramping up. The spectrogram is analyzed to choose initial andtarget frequencies for the order filters to enhance only one harmonic(e.g., a single order), while maintaining the quality factor Q and thegain constant between the initial and target filters. The filteredspectrogram 520 depicts the signal after filtering according to thedigital signal processing method 400 with coefficient morphing asmentioned hereinabove for every sample. Thus, as the frequency ramps upas depicted, the order filters may filter out a desired harmonic inreal-time without audible transients or undesirable effects. The filtersperform well even when changing parameters, such as RPM, rapidly.

Referring again to FIG. 4 , after order filtering each channel based onthe operating conditions, the filtered output is passed throughcorresponding equalization (EQ) filters 422 to further filter out oreliminate high-frequency content. The EQ filters 422 thus reinforce theorder filters 420. The EQ filters 422 are tunable, and up to ten EQfilters for each order may be provided, depending on the application.The EQ filters 422 may comprise low-pass filters.

After EQ filtering at 420, the four filtered channels are then mixed viaa tunable order mixer 424 into a single mono output. After summing thefiltered signals into the mono signal, the gain of the mono signal isadjusted. For example, based on the RPM and torque measurements of theCAN signals 412, a main gain is obtained from a three-dimensional maingain lookup table 426, and the gain of the mono signal is adjustedaccording to the main gain. The gain-adjusted signal is then upsampled432 to the original sampling rate of the sensor input 402, for exampleby a factor L, and then upmixed 434 to a plurality of channels asdepicted. For example, the signal may be upmixed 434 to four channels,with one channel for each speaker of the plurality of speakers 450 thatwill output the enhanced engine sound, though it should be appreciatedthat the method 400 may be adapted for a number of channels andrespective speakers greater than four or less than four.

Delays 440 are applied to each channel based on the relativedistribution of the speakers 450 throughout the cabin of the vehicle,such that enhanced engine sound is perceived as coming from the engine.For example, if the engine is positioned in the front of the vehicle,the signals may be delayed such that an occupant of the vehicleperceives the enhanced engine sound as coming from the front of thevehicle. Similarly, if the engine is positioned in the rear of thevehicle, the signals may be delayed such that the occupant perceives theenhanced engine sound as coming from the rear of the vehicle.

In addition, a limiter 442 may be applied to the signals, such that ifone of the channel levels needs to be decreased, the other channels maybe adjusted as well, thereby balancing the signals. After passing thesignals through the limiter 442, the signals are output to respectivespeakers 450 of the vehicle. The signals may be added to the normalaudio content (e.g., radio or other musical playback, other audioplayback such as navigation prompts, warning chimes, and so on) alreadybeing output to the speakers 450. By delaying and limiting the signalsas described hereinabove prior to mixing the signals into thepre-existing audio output of the speakers 450, the enhanced engine soundcomprising the signals may create the spatial image regardless of audiobalancing for the audio system including the speakers 450. For example,audio such as music may be played back through the speakers 450 withbalanced levels and a stereo audio distribution, while the enhancedengine sound signals superimposed onto the musical audio is perceivedwith the spatial image or spatial effect such that the engine soundgenerated by the engine is enhanced with the enhanced engine sound.

As indicated by the legend, the delays 440 and the limiter 442 may alsobe tunable according to the desired application or configuration of thevehicle (e.g., the configuration of the engine, the configuration andnumber of the speakers, and so on). It should be appreciated that someparameters, such as the EQ filters 422, the order mixer 424, the delay440, and the limiter 442 may be tuned once based on the desiredapplication or configuration of the vehicle, and do not change in realtime. Other parameters change in real-time when a new CAN messagearrives, for example, to change the harmonics filters. While the CANprotocol normally works at a rate of 10 ms or 50 ms, in order to avoidde-synchronization between the actual engine sound and the output of thesignal processing, the CAN protocol preferably operates at 10 ms. Theparameters that may be tuned in real-time are thus the order frequency,the 3D gain table, the 3D quality factor table, and the 3D main gaintable.

As another illustrative and non-limiting example, FIG. 6 is a blockdiagram illustrating another example digital signal processing chain 600for enhanced vehicle sound synthesis. A sensor input 602, such as thesignal from a sensor such as an accelerometer, is downsampled 604, andthen upmixed 606 to a desired number of channels. In the depictedexample, the signal is upmixed to fourteen channels for fourteen orders.Selectively filtering such a number of filters for such a number oforders enables a more fine-tuned control over the enhancement of theengine sound. To that end, CAN signals such as the RPM measurement 610and the throttle position 612 may be used to adjust the order filters620 for each order based on a plurality of lookup tables 616. Forexample, as depicted, the RPM 610 may be used to determine a centerfrequency (f) for each order. Further, the RPM 610 and the throttleposition 612 may be used to determine a gain (G) for each order and aquality factor (Q) for each order. The lookup tables 616 may be tunedaccording to the desired enhancement of engine orders based on the RPMand the throttle position. Each order filter 620 is therefore adjustedto target a specific order. After order filtering at 620, the fourteenfiltered signals may be mixed or summed via the order mixer 622 into amono output. The gain of the mono output is adjusted as desired at 624,and then upmixed 626 into a desired number of channels. The signal foreach channel is then filtered, for example with a tunable biquad filter630, prior to outputting the signals to speakers 640.

To illustrate how the order filters may be adjusted for each order,FIGS. 7A-7D depict different order filters for four different orders. Inparticular, FIG. 7A shows a set of graphs 700 illustrating examplelookup tables for determining an example first order filter for a firstorder. The set of graphs 700 include a graph 702 illustrating a firstorder filter for the first order. An example three-dimensional gainlookup table that outputs a gain for a given RPM and torque measurementis depicted as two two-dimensional lookup tables, namely the gain-RPMlookup table 704 and the gain-torque lookup table 706. Similarly, anexample three-dimensional quality factor lookup table that outputs aquality factor Q for a given pair of RPM and torque measurements isdepicted as two two-dimensional lookup tables, namely the Q-RPM lookuptable 708 and the Q-torque lookup table 710. The gain and Q factors forthe first order filter depicted in graph 702 are thus determined basedon the RPM measurement 712 and the torque measurement 714. Further, thecenter frequency of the first order filter depicted in the graph 702 isdetermined based on the RPM measurement 712.

Similarly, FIG. 7B shows a set of graphs 720 illustrating example lookuptables for determining an example second order filter for a secondorder. The set of graphs 720 include a graph 722 illustrating a secondorder filter for the second order, as well as a gain-RPM lookup table724, a gain-torque lookup table 726, a Q-RPM lookup table 728, and aQ-torque lookup table 730 for the second order. The gain and Q factorsfor the second order filter depicted in graph 722 are thus determinedbased on the RPM measurement 712 and the torque measurement 714.Further, the center frequency of the second order filter depicted in thegraph 722 is determined based on the RPM measurement 712.

FIG. 7C shows a set of graphs 740 illustrating example lookup tables fordetermining an example third order filter for a third order. The set ofgraphs 740 include a graph 742 illustrating a third order filter for thethird order, as well as a gain-RPM lookup table 744, a gain-torquelookup table 746, a Q-RPM lookup table 748, and a Q-torque lookup table750 for the third order. The gain and Q factors for the third orderfilter depicted in graph 742 are thus determined based on the RPMmeasurement 712 and the torque measurement 714. Further, the centerfrequency of the third order filter depicted in the graph 742 isdetermined based on the RPM measurement 712.

FIG. 7D shows a set of graphs 760 illustrating example lookup tables fordetermining an example fourth order filter for a fourth order. Inparticular, the set of graphs 760 include a graph 762 illustrating afourth order filter for the fourth order, as well as a gain-RPM lookuptable 764, a gain-torque lookup table 766, a Q-RPM lookup table 768, anda Q-torque lookup table 770 for the fourth order. The gain and Q factorsfor the fourth order filter depicted in graph 762 are thus determinedbased on the RPM measurement 712 and the torque measurement 714.Further, the center frequency of the fourth order filter depicted in thegraph 762 is determined based on the RPM measurement 712.

FIG. 8 shows a high-level flow chart illustrating an example method 800for enhanced vehicle sound synthesis. The method 800 may be implemented,for example, as the digital signal processing method 400 in thecomputing system 150, as a non-limiting example.

Method 800 begins at 805. At 805, method 800 receives a sensor signal,such as the sensor input 402 from the sensor 144. Further, at 810,method 800 receives measurements of RPM and torque, for example via theCAN bus 136. At 815, method 800 downsamples the sensor signal. At 820,method 800 upmixes the downsampled sensor signal into a number ofchannels according to a number of orders. At 825, method 800 determinesa gain value and a Q value for each order based on the RPM and torque,for example by retrieving the gain values and Q values from the lookuptables 414 and 416. Further, at 830, method 800 determines a centerfrequency for each order based on the RPM, for example by retrievingcenter frequencies for each order from the order lookup table 418.

At 835, method 800 determines an order filter for each order based onthe gain, Q value, and center frequency. Each order filter may bedifferent, as described hereinabove with regard to FIGS. 7A-7D. Further,the filter coefficients may also be determined according to filtercoefficient morphing in order to maintain stability and preventtransient frequencies from passing through. At 840, method 800 applieseach order filter to a corresponding channel of the downsampled sensorsignal. Further, at 845, method 800 applies an equalization filter toeach order filtered channel to filter out high-frequency content. Afterfiltering each channel, method 800 continues to 850. At 850, method 800mixes the equalized signals into a single channel output. At 855, method800 determines a main gain based on the RPM and torque. At 860, method800 adjusts the gain of the single channel output based on the maingain. At 865, method 800 upsamples the gain-adjusted single channeloutput. At 870, method 500 upmixes the upsampled signal into a pluralityof channels, including one channel for each speaker. At 875, method 800adjusts a delay for each channel based on speaker position. At 880,method 800 applies a limiter to the signals to balance the levels. At885, method 800 outputs the signals to a plurality of speakers. Method800 then returns.

Thus, in one embodiment, a method for a vehicle comprises acquiring,from a sensor configured to measure engine sounds of an engine of thevehicle, the measured engine sounds, filtering the measured engine soundbased on operating conditions of the engine to obtain an enhanced enginesound, and outputting, to a speaker positioned in a cabin of thevehicle, the enhanced engine sound.

In a first example of the method, filtering the measured engine soundbased on the operating conditions of the engine to obtain the enhancedengine sound comprises upmixing the measured engine sound into aplurality of channels for a given number of engine orders, adjusting anorder filter for each engine order of the given number of engine ordersbased on the operating conditions of the engine, filtering each channelof the plurality of channels with the corresponding order filter, andmixing the filtered channels into a mono output comprising the enhancedengine sound. In a second example of the method optionally including thefirst example, adjusting the order filter for each engine order based onthe operating conditions of the engine comprises adjusting a gain and aquality factor for each order filter based on measurements ofrevolutions per minute (RPM) and torque of the engine, and adjusting acenter frequency for each order filter based on the RPM. In a thirdexample of the method optionally including one or more of the first andsecond examples, the method further comprises filtering each channelwith a low-pass filter prior to mixing the filtered channels into themono output. In a fourth example of the method optionally including oneor more of the first through third examples, the method furthercomprises upmixing the mono output into a second plurality of channels,and applying a separate delay to each channel of the second plurality ofchannels, wherein outputting the enhanced engine sound to the speakercomprises outputting the delayed channels to respective speakers in thevehicle.

In another embodiment, a method for a vehicle comprises acquiring asignal including harmonic content generated by an engine of the vehicle,upmixing the signal into a plurality of channels for a given number ofengine orders, adjusting an order filter for each engine order of thegiven number of engine orders based on operating conditions of theengine, filtering each channel of the plurality of channels with thecorresponding order filter, mixing the filtered channels into a monooutput, and outputting the mono output to at least one speaker in thevehicle.

In a first example of the method, acquiring the signal comprisesacquiring the signal via an accelerometer mounted to the engine. In asecond example of the method optionally including the first example,adjusting the order filter for each engine order based on the operatingconditions of the engine comprises adjusting a gain and a quality factorfor each order filter based on measurements of revolutions per minute(RPM) and torque of the engine, and further adjusting a center frequencyfor each order filter based on the RPM. In a third example of the methodoptionally including one or more of the first and second examples, themethod further comprises filtering each channel with a low-pass filterprior to mixing the filtered channels into the mono output. In a fourthexample of the method optionally including one or more of the firstthrough third examples, the method further comprises adjusting a maingain of the mono output based on measurements of RPM and torque of theengine. In a fifth example of the method optionally including one ormore of the first through fourth examples, the method further comprisesupmixing the mono output into a second plurality of channels, andapplying a separate delay to each channel of the second plurality ofchannels, wherein outputting the mono output to at least one speaker inthe vehicle comprises outputting the delayed channels to respectivespeakers in the vehicle. In a sixth example of the method optionallyincluding one or more of the first through fifth examples, the methodfurther comprises running the delayed channels through a limiter tobalance levels prior to outputting the delayed channels to therespective speakers in the vehicle. In a seventh example of the methodoptionally including one or more of the first through sixth examples,the mono output is output to the at least one speaker in the vehiclewithin 10 milliseconds of acquiring the signal.

In yet another embodiment, a system for a vehicle comprises a sensorconfigured to measure engine sounds of an engine of the vehicle, aspeaker positioned in a cabin of the vehicle, and a computing systemconfigured to: acquire, from the sensor, the measured engine sounds;apply filters to the measured engine sound based on operating conditionsof the engine to obtain an enhanced engine sound; and output, to thespeaker, the enhanced engine sound.

In a first example of the system, the sensor comprises an accelerometer,and wherein the measured engine sound comprises vibrations generated bythe engine. In a second example of the system optionally including thefirst example, to apply the filters to the measured engine sound basedon the operating conditions of the engine to obtain the enhanced enginesound, the computing system is further configured to: upmix the measuredengine sound into a plurality of channels for a given number of engineorders; adjust an order filter for each engine order of the given numberof engine orders based on the operating conditions of the engine; filtereach channel of the plurality of channels with the corresponding orderfilter; and mix the filtered channels into a mono output comprising theenhanced engine sound. In a third example of the system optionallyincluding one or more of the first and second examples, to adjust theorder filter for each engine order based on the operating conditions ofthe engine, the computing system is further configured to: adjust a gainand a quality factor for each order filter based on measurements ofrevolutions per minute (RPM) and torque of the engine, and adjust acenter frequency for each order filter based on the RPM. In a fourthexample of the system optionally including one or more of the firstthrough third examples, the computing system is further configured to:filter each channel with a low-pass filter prior to mixing the filteredchannels into the mono output. In a fifth example of the systemoptionally including one or more of the first through fourth examples,the system further comprises a plurality of speakers including thespeaker, wherein the computing system is further configured to: upmixthe mono output into a second plurality of channels; and apply aseparate delay to each channel of the second plurality of channels,wherein outputting the enhanced engine sound to the speaker comprisesoutputting the delayed channels to respective speakers in the vehicle.

The description of embodiments has been presented for purposes ofillustration and description. Suitable modifications and variations tothe embodiments may be performed in light of the above description ormay be acquired from practicing the methods. For example, unlessotherwise noted, one or more of the described methods may be performedby a suitable device and/or combination of devices, such as the vehiclesystems described above with respect to FIGS. 1 and 2 . The methods maybe performed by executing stored instructions with one or more logicdevices (e.g., processors) in combination with one or more hardwareelements, such as storage devices, memory, hardware networkinterfaces/antennas, switches, actuators, clock circuits, and so on. Thedescribed methods and associated actions may also be performed invarious orders in addition to the order described in this application,in parallel, and/or simultaneously. The described systems are exemplaryin nature, and may include additional elements and/or omit elements. Thesubject matter of the present disclosure includes all novel andnon-obvious combinations and sub-combinations of the various systems andconfigurations, and other features, functions, and/or propertiesdisclosed.

As used in this application, an element or step recited in the singularand proceeded with the word “a” or “an” should be understood as notexcluding plural of said elements or steps, unless such exclusion isstated. Furthermore, references to “one embodiment” or “one example” ofthe present disclosure are not intended to be interpreted as excludingthe existence of additional embodiments that also incorporate therecited features. The terms “first,” “second,” “third,” and so on areused merely as labels, and are not intended to impose numericalrequirements or a particular positional order on their objects. Thefollowing claims particularly point out subject matter from the abovedisclosure that is regarded as novel and non-obvious.

The invention claimed is:
 1. A method for a vehicle, comprising:acquiring, from a sensor configured to measure engine sounds of anengine of the vehicle, the measured engine sounds; filtering themeasured engine sound based on operating conditions of the engine toobtain an enhanced engine sound, including: upmixing the measured enginesound into a plurality of channels for a given number of engine orders,adjusting an order filter for each engine order of the given number ofengine orders based on the operating conditions of the engine, filteringeach channel of the plurality of channels with the corresponding orderfilter, and mixing the filtered channels into a mono output comprisingthe enhanced engine sound, wherein the order filter for each engineorder corresponds with a multiple of a number of ignition events perrevolution of a crankshaft of the engine of the vehicle; and outputting,to a speaker positioned in a cabin of the vehicle, the enhanced enginesound.
 2. The method of claim 1, wherein adjusting the order filter foreach engine order based on the operating conditions of the enginecomprises: adjusting a gain and a quality factor for each order filterbased on measurements of revolutions per minute (RPM) and torque of theengine; and adjusting a center frequency for each order filter based onthe RPM.
 3. The method of claim 1, further comprising: upmixing the monooutput into a second plurality of channels; and applying a separatedelay to each channel of the second plurality of channels, whereinoutputting the enhanced engine sound to the speaker comprises outputtingthe delayed channels to respective speakers in the vehicle.
 4. A methodfor a vehicle, comprising: acquiring a signal including harmonic contentgenerated by an engine of the vehicle; upmixing the signal into aplurality of channels for a given number of engine orders; adjusting anorder filter for each engine order of the given number of engine ordersbased on operating conditions of the engine; filtering each channel ofthe plurality of channels with the corresponding order filter and with alow-pass filter; mixing the filtered channels into a mono output; andoutputting the mono output to at least one speaker in the vehicle. 5.The method of claim 4, wherein acquiring the signal comprises acquiringthe signal via an accelerometer mounted to the engine.
 6. The method ofclaim 4, wherein adjusting the order filter for each engine order basedon the operating conditions of the engine comprises adjusting a gain anda quality factor for each order filter based on measurements ofrevolutions per minute (RPM) and torque of the engine, and furtheradjusting a center frequency for each order filter based on the RPM. 7.The method of claim 4, further comprising adjusting a main gain of themono output based on measurements of RPM and torque of the engine. 8.The method of claim 4, further comprising upmixing the mono output intoa second plurality of channels, and applying a separate delay to eachchannel of the second plurality of channels, wherein outputting the monooutput to at least one speaker in the vehicle comprises outputting thedelayed channels to respective speakers in the vehicle.
 9. The method ofclaim 8, further comprising running the delayed channels through alimiter to balance levels prior to outputting the delayed channels tothe respective speakers in the vehicle.
 10. The method of claim 4,wherein the mono output is output to the at least one speaker in thevehicle within 10 milliseconds of acquiring the signal.
 11. The methodof claim 4, further comprising mixing the mono signal into normal audiooutput to the at least one speaker.
 12. A system for a vehicle,comprising: a sensor configured to measure engine sounds of an engine ofthe vehicle; a speaker positioned in a cabin of the vehicle; and acomputing system configured to: acquire, from the sensor, the measuredengine sounds; apply filters to the measured engine sound based onoperating conditions of the engine to obtain an enhanced engine sound,including to: upmix the measured engine sound into a plurality ofchannels for a given number of engine orders, adjust an order filter foreach engine order of the given number of engine orders based on theoperating conditions of the engine, and filter each channel of theplurality of channels with the corresponding order filter and with alow-pass filter; and output, to the speaker, the enhanced engine sound.13. The system of claim 12, wherein the sensor comprises anaccelerometer, and wherein the measured engine sound comprisesvibrations generated by the engine.
 14. The system of claim 12, wherein,to apply the filters to the measured engine sound based on the operatingconditions of the engine to obtain the enhanced engine sound, thecomputing system is further configured to: mix the filtered channelsinto a mono output comprising the enhanced engine sound.
 15. The systemof claim 14, wherein, to adjust the order filter for each engine orderbased on the operating conditions of the engine, the computing system isfurther configured to: adjust a gain and a quality factor for each orderfilter based on measurements of revolutions per minute (RPM) and torqueof the engine; and adjust a center frequency for each order filter basedon the RPM.
 16. The system of claim 14, further comprising a pluralityof speakers including the speaker, wherein the computing system isfurther configured to: upmix the mono output into a second plurality ofchannels; and apply a separate delay to each channel of the secondplurality of channels, wherein outputting the enhanced engine sound tothe speaker comprises outputting the delayed channels to respectivespeakers in the vehicle.